1. Field of the Invention
The present invention relates to medical implantable device, and more particularly, to a vascular occlusive device, such as an embolic coil for occluding an aneurysm, which includes a bioactive coating placed on the occlusive device for reacting with bodily tissue in order to promote a desired result, for example promoting an increase of tissue growth into the occlusive device.
2. Description of the Prior Art
For many years vasculature occlusive devices have been placed within the vasculature of the human body to occlude, or partially occlude, blood flow through the vasculature. Additionally, such devices have been introduced into aneurysms in order to fill, or partially fill, the aneurysm so as to reduce the pressure which is applied to the interior of the aneurysm in order to prevent further growth or expansion of the aneurysm. These devices may take the form of a coil, such as a helical coil, and are typically placed within the vessel or aneurysm by use of a delivery catheter which is inserted into the vessel and positioned such that the distal end of the delivery catheter is adjacent to a selected site for placement. Once the occlusive device is placed within a blood vessel or aneurysm, surrounding tissue reacts with the “foreign” object and begins to grow into and around the device to provide more complete occlusion of the vessel.
Examples of such delivery catheters are disclosed in U.S. Pat. No. 5,108,407, entitled “Method And Apparatus For Placement Of An Embolic Coil” and U.S. Pat. No. 5,122,136, entitled “Endovascular Electrolytically Detachable Guidewire Tip For The Electroformation Of Thrombus In Arteries, Veins, Aneurysms, Vascular Malformations And Arteriovenous Fistulas.” These patents disclose catheter systems for delivering embolic coils to preselected positions within vessels of the human body in order to treat aneurysms, or alternatively, to occlude a blood vessel at a preselected location.
Occlusive devices which take the form of coils may be helically wound coils, random wound coils, coils wound within coils or other such coil configurations. Examples of various coil configurations are disclosed in U.S. Pat. No. 5,334,210, entitled, “Vascular Occlusion Assembly” and U.S. Pat. No. 5,382,259, entitled, “Vasoocclusion Coil With Attached Tubular Woven Or Braided Fibrous Covering.” Such coils are generally formed from radiopaque metallic materials, such as platinum, gold, tungsten or alloys of these metals. Oftentimes several coils are placed at a given location within a vessel, or within an aneurysm, to more completely occlude, or partially occlude, the flow of blood through the vessel or aneurysm. Thrombus growth onto the coils further enhances the occlusive effect of the coils.
In the past, embolic coils have been placed within the distal end of a delivery catheter and when the distal end of the catheter is properly positioned, the coil may then be pushed out of the end of the catheter with, for example a guidewire, to release the coil at the desired location. This procedure of placement of the embolic coil is conducted under fluoroscopic visualization such that the movement of the coil may be monitored and the coil may be placed at a desired location.
In addition, such coils have been specifically designed to be stretch resistant, such as the vasculature occlusive coil disclosed in U.S. Pat. No. 5,853,418, entitled, “Stretch Resistant Vaso-Occlusive Coils (II)” which discloses a helically wound coil having a polymeric stretch resistant member extending through the lumen of the coil and fixedly attached to both ends of the coil to prevent the coil from stretching.
In order to increase the thrombogenicity of an embolic coil, such coils have included a coating, such as collagen, which is applied to the surface of the coil. This concept is disclosed in U.S. Pat. No. 5,690,671, entitled, “Embolic Elements And Methods And Apparatus For Their Delivery,” which discloses such a collagen coated embolic coil.
In addition, U.S. Pat. No. 5,980,550, entitled, “Water-Soluble Coating For Bioactive Vasoocclusive Devices,” discloses an embolic coil having an inner coating which serves as a thrombogenic agent and an outer coating of a water soluble agent which dissolves after placement of the coil in order expose the thrombogenic inner coating to enhance the growth of thrombus into an around the coil.
The water soluble coating prevents the thrombogenic inner coating from coming into contact with the surrounding blood until the water soluble coating is dissolved by contact with blood which is comprised largely of water.
While the vasculature occlusive device disclosed in this patent includes an agent for enhancing thromboginicity of the device and also includes an outer coating to prevent such activity until the outer coating is dissolved by blood flow, there is no control over when the dissolving process begins and therefore no control over the time in which the thrombogenic agent becomes activated. Without such control, it is possible that thrombus can begin forming on the coil prior to the time the coil is properly placed within a vessel, or aneurysm, therefore making it very difficult if not impossible to reposition, or remove, the improperly placed coil. Alternatively, with water soluble outer protective coating the passive process of removing the outer coating may be so slow that the reaction may not occur in a timely manner.